Found this old info on a guy running a 6758 or 6258 on an SR20:
http://zilvia.net/f/builds-builds-on...ml#post4685523
Not sure which because he said 6758 initially and then said 6258. Also, he never specified if it's at full boost or just entering boost by 3k. Either way, that's responsive and it did 367whp on 18psi which is a good number for that much boost. 500whp on a 6758 is going to be hard to reach though.
Check out how it maps on a 6758:
HERE
25psi at 7500rpm is pretty much exactly the limit of the 6758's flow. Any higher revs and you're gonna drop boost while the 7163 can hold 25psi to 8500rpm or 30psi to the same 7500rpms.